Torque distribution device

ABSTRACT

A differential drive that includes a rotatably driven differential housing supported in a housing. The differential drive further includes a differential gear set arranged and supported in the differential housing. The differential drive also includes a torque distribution device adjacent to a differential gear set. The torque distribution device connects a differential side shaft gear with one side shaft. The torque distribution device is arranged to control the torque between a front axle and a rear axle of a motor vehicle.

This application is a continuation of Ser. No. 09/492,988 filed Jan. 27,2000, now U.S. Pat. No. 6,296,590.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to differential drives for a motorvehicle, and more particularly, relates to an active torque transferdevice for use in a vehicle.

2. Description of Related Art

The differential drive is well known in the motor vehicle industry. Thedifferential drive is used in conjunction with the transmission anddrive shaft or propeller shaft (prop shaft) to turn the automotivevehicle wheels at different speeds when the vehicle is going around acurve, to differentiate the speed of each wheel individually and toprovide the proper amount of torque to each wheel in slipping, turning,or other road to wheel conditions.

In a traditional torque on demand drive train layout of an automotivevehicle there is a primary driven front/rear axle and a secondary driven“hang on” axle that is connected via a prop shaft or drive shaft and atorque transfer coupling to the primary driven axle. The torque transfercoupling is usually directly in front of the secondary driven axle. Theaxle differential creates the division of power (or torque) to each sideshaft of the axle. The primary driven axle also includes a differentialwhich divides necessary power to the side shaft of each front axle andthen the wheels. The division of torque between the front and rear axleis completed by the torque transfer coupling which is a separate unit onthe drive train system and requires space for its housing and otherrelated parts. A current state of the art torque transfer coupling foran automotive vehicle is located between the primary and secondarydriven axles of the vehicle and, generally consists of a friction clutchpack which is loaded via a ball ramp mechanism. The ball ramp mechanismis engaged by an electric motor. An electronic control unit senses slipconditions of the wheels, monitors current driving conditions of thevehicle and applies a current to the electric motor which will engagethe clutch via the ball ramp mechanism and distribute torque to eachwheel as necessary.

An active torque transfer system provides maximum flexibility in thedistribution of torque between the axles of an all wheel or four wheeldrive automotive system. A similar system can be used in applying torquewithin an axle on a side to side basis between a left rear wheel and aright rear wheel. Other devices currently used in the art for activetorque transfer include electromagnetically engaged pilot clutch todrive a ball ramp mechanism. This mechanism loads the main clutch viaelectromagnetically engaged pilot clutches. Most of the systems use thesame ball ramp mechanism but use different engagement mechanisms toengage the ball ramp mechanism to the clutch unit. All of these activetorque drive systems are located in a separate housing usually directlyin front of the rear (differential in most cases.

Therefore, there is a need in the art for a device to simplify andreduce the weight and required space of an active torque distributiondevice for use in an automotive vehicle.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved torquedistribution device.

Another object of the present invention is to provide a torquedistribution device that includes a clutch pack that runs at axle speed,which will reduce imbalance issues to the transaxle.

Yet a further object of the present invention is to reduce the packagingrequirement in the propeller shaft area of the automotive vehicle.

Still another object of the present invention is to provide adifferential that does not require a separate oil housing for a clutchpack, but also reduces or minimizes the effort for the bearings andseals.

A further object of the present invention is to reduce the number ofinterfaces in the drive train while also reducing the weight and cost ofthe drive train assembly.

Still a further object of the present invention is to integrate withinthe existing axle housing the engagement mechanism needed to control thetorque between the front and rear axles.

Still a further object of the present invention is to combine the frontto rear and side to side locking features of a drive train system withinone system unit.

To achieve the foregoing objects the differential drive for use on avehicle includes a rotatably driven differential housing supported in anaxle housing. A differential gear set arranged and supported in thedifferential housing. A torque distribution device adjacent to thedifferential gear set. The torque distribution device connects onedifferential side shaft gear with one side shaft. The torquedistribution device is arranged to control the torque between a frontaxle and a rear axle of the automotive vehicle.

One advantage of the present invention is a new and improved torquedistribution device for a vehicle.

A further advantage of the present invention is that the torquedistribution device uses a clutch pack that runs with axle speed whichreduces imbalance issues throughout the transaxle.

A further advantage of the present invention is the reduced packagingrequirement in the prop shaft area of the drive train system.

Still a further advantage of the present invention is the inclusion ofthe clutch pack within the housing of the differential thus requiring noseparate oil housing and also reducing the effort for bearings and sealswhile improving the cooling of the clutch pack.

Another advantage of the present invention is the reduced number ofinterfaces within the drive train system and the reduced weight andcosts of distributing torque to the drive train system.

A further advantage of the present invention is the integration withinthe axle housing of the engagement mechanism for the torque distributiondevice.

A further advantage of the present invention is the combination of frontto rear and side to side locking control features within one system.

Other objects, features, and advantages of the present invention willbecome apparent from the subsequent description and appended claimstaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a vehicle system according to thepresent invention.

FIG. 2 shows a schematic view of a vehicle drive train system accordingto the present invention.

FIG. 3A shows a cross section through a differential drive according tothe present invention.

FIG. 3B shows a cross section through a differential drive including anoptional second clutch pack according to the present invention.

FIG. 4 shows an alternate embodiment in partial cross section of thepresent invention.

FIG. 5 shows a cross section of a two pinion differential.

FIG. 6 shows a cross section of an alternate embodiment of a threepinion differential.

FIG. 7 shows an exploded view of the engagement mechanism used in thepresent invention.

BEST MODE OF CARRYING OUT THE INVENTION AND DESCRIPTION OF THE PREFERREDEMBODIMENT(S)

Referring to the drawings, a torque distribution device 10 according tothe present invention is shown. FIG. 1 schematically illustrates an allwheel drive or four wheel drive motor vehicle 12 that is a primary frontwheel driven vehicle, however, the present invention can be used on aprimary rear wheel driven vehicle as well.

The motor vehicle 12 as shown in FIG. 1 is primarily driven by a frontaxle 15. The motor vehicle 12 is an all wheel or four wheel drivevehicle and is driven by power transferred from the engine 16 through atransaxle or gear box 18 which may be either automatic or a manual gearbox, into the power take off 20 of the drive train assembly and finallyon through to the first differential 30 and when demanded to the reardifferential 22 via a propeller shaft or driving shaft 24, whichtransfers power to the rear differential 22. At the rear differential 22power is split to a left hand rear side shaft 26 and a right hand rearside shaft 28 for distribution to the wheels at the rear of the vehicle.The front differential 30 controls power and slip or spin from the lefthand front side shaft 32 and the right hand front side shaft 34. In anall wheel drive vehicle power is delivered to both the rear differential22 and the front differential 30 via a distributing drive, but eitherthe front axle 15 or rear axle 14 is the primary driven axle, with theother axle only receiving most of the power when needed. The preferredembodiment of the present invention is an all wheel drive vehiclewherein the torque distribution device 10 is located within the reardifferential 22 and acts from there to distribute torque to the frontand rear axles of the vehicle.

FIG. 2 shows the drive train 36 of an all wheel drive vehicle. The drivetrain 36 includes a front axle 15 which includes the left hand frontside shaft 32 and the right hand front side shaft 34. The propellershaft or drive shaft 24 transmits power from the power take off 20 tothe rear differential 22. The rear differential 22 has a left hand rearside shaft 26 and a right hand rear side shaft 28 extending therefrom tothe vehicle wheels which will drive the vehicle in a forward or reversemotion. The rear differential drive 20 includes an axle housing 40 inwhich a differential housing 42 is rotatably supported around arotational axis. The differential housing 42 is driven by the vehiclegear box via a driving gear 44. The torque distribution device 10 of thecurrent invention is located within the differential housing 40 and isused to actively transfer torque between the front axle 15 and the rearaxle 14 as shown in FIG. 2. The use of the torque distribution device 10within the differential drive 22 in conjunction with an opendifferential 42 will reduce the weight and cost of the car by removingthe need of a torque transfer coupling which is usually located directlyin front of the rear differential drive. The incorporation of the torquetransfer device 10 within the differential drive 22 greatly reduces thespace required on the undercarriage of the car leaving more space forexhaust and fuel tank needs.

FIGS. 3A and 3B show a cross section of the differential drive 22 whichincludes the axle housing 40 which rotatably supports the differentialhousing 42 around a rotational axis. Within the differential housing 42,a differential gear set 48 is rotatably arranged and supported. In thepreferred embodiment the differential gear set 48 is a standard bevelore planetary set. This gear set 48 generally includes two differentialbevel gears 50, 52 that are rotatably arranged on a bearing pin 54 whichaxis forms a rotational axis for the two differential bevel gears 50,52. The rotational axis for the differential bevel gears or differentialgears 50, 52 will intersect the rotational axis for the differentialside shaft gears 56, 58 within the differential housing 42. Thedifferential housing 42 includes two differential side shaft gears 56,58 that are arranged around a rotational axis as to be rotatablerelative to the differential housing 42. The differential side shaft orside shaft gears 56, 58 are rotatably received in bores 60 of thedifferential housing 42. The side shaft gears are supported against theinterfaces of the differential housing 42 with supporting discs 62arranged therebetween. The axis of rotation of the side shaft gears 56,58 and the axis of rotation of the differential gears 50, 52 intersecteach other at a right angle. The propeller shaft or drive shaft 24engages the differential housing 42 via a driving gear 44.

The torque distribution device 10 is located within the differentialhousing 42 and engages the differential gear set 48. The torquedistribution device 10 will connect one of the differential side shaftgears 58 with one of the side shafts 28. The torque distribution device10 includes a clutch pack 64 which in the preferred embodiment is afriction clutch pack as shown in FIG. 3A. The friction clutch pack 64includes a first end housing (outer face) 66 and an inner hub 68 towhich friction plates 70 are attached in an alternating fashion so as tooverlap with each other. A pressure ring 72 engages one end of thefriction pack clutch 64 and will provide the engagement onto the clutchto control the torque between the one side shaft gear 58 and one sideshaft 28. The pressure ring 72 is activated by a pin 74 and spring 76combination which is in turn controlled by an engagement mechanism 78 asshown in FIG. 7.

The engagement mechanism 78 is a ball ramp type mechanism which isengaged by an electric motor 80. As shown in FIG. 7 an electric motor 80includes reduction gearing 84 which transmits forces through an expanderdisc 82. The expander disc 82 includes a plurality of circumferentialextending grooves 86. Connected to the expander disc 82 is a pressuredisc 88 which has expander balls 90 with ball ramps placed therebetween, such that the expander balls 90 are disposed one in each of theextending grooves 86. Engaging the pressure disc 88 on a side oppositethe expander disc 82 is a thrust race ring 92. A pressure ring 94 whichconnects through to the friction discs 96 of the expander mechanism 78.An electronic control unit 98 is connected to the electric motor 80 andalso connected to the wheels of the vehicle. The electronic control unit98 monitors the driving conditions being encountered by the vehicle andwill sense any slip conditions or other driving conditions and apply acurrent to the electronic motor 80 based on reactions to the slipconditions sensed in the wheels. The expansion of the expansionmechanism will engage the pin 74 and spring 76 which will depress thepressure ring 72 and engage the clutch pack 64 which is in contact withthe vehicle side shaft gear 58 and side shaft 28.

As shown in FIG. 3A the differential gear set 48 will take the speeddifference between the front and rear driven axle and between the leftand right hand wheels of the secondary driven or rear axle at the sametime. This all occurs while the clutch pack 64 is running at the samespeed as the axle speed and providing the torque transfer to one sideshaft 28 and then onto a wheel. The second side gear shaft 56 and theconnected side shaft 26 and wheel, is then driven with the same torquevia the open differential. Therefore, the differential acts as an opendifferential between the left and right side shafts of the axle allowingthe wheels to spin freely. FIG. 3A shows the engagement mechanism, whichis a ball ramp mechanism in our preferred embodiment, attached to thedifferential case 42 and therefore causes no added load on the bearings100 of the differential drive. The torque distribution device 10 asdescribed above controls the slip between the front and rear axles ofthe automotive vehicle by controlling one of the side shafts 28 of thesecondary driven axle. This removes the need for a separate torquetransfer coupling which is generally located directly in the prop shaftusually in front of the rear differential drive. As shown in FIG. 3B itshould also be noted that within the differential housing 42 is locateda second set of friction plates that are engaged between the side shaftgear 58 and the differential housing 42 which will provide additionalside to side locking control between the right hand wheel and the lefthand wheel of the side shaft, respectively. Therefore, the torquedistribution device 10 as described above including the second clutchpack or friction plates 102 can combine and control both front to rearand side to side locking effects. The locking effects controlled betweenthe front to rear and side to side by the torque distribution device 10can be set up in a ratio such that you can tulle the device 10 byadjusting the number of friction plates used for each function, i.e.,front to rear torque control and side to side torque or locking effectcontrol.

FIG. 4 shows an alternate embodiment of the present invention whereinthe engagement mechanism 278 is located within the axle housing in whichcase the right hand taper bearing 200 is loaded with the engagementforce of the motor and ball ramp engagement mechanism 278. The ball rampengagement mechanism 278 works the same way as described above. As shownin FIG. 4 the differential gear set 248 is rotatably mounted within thedifferential housing 242. The differential bevel gears 250 are mountedon a smaller bearing pin 254 and are in contact with the differentialside shaft gears 256, 258. Positioned between the side shaft gears 256,258 is located a thrust bearing 263 to keep the side shaft gears 256,258 from rubbing against each other causing unwanted noise. The reducedpin differential gear sets 248 have at least two differential gears 250,252 but may have more depending on the design of the differentialhousing 242. The differential gear 250 is allowed to move small amountsto adjust to the interaction between the side shaft gears 256, 258 andthe differential gears 250, 252. The clutch pack 284 is arranged in thesame manner as found in the above embodiment. The second clutch pack 302which is used to control side to side spinning and torque on the axle isengaged between the side shaft gear 256 and the differential housing242.

FIG. 5 and FIG. 6 show cross sections of the differential gear set 248as described in the embodiment shown in FIG. 4. FIG. 5 shows the two pindifferential gear set 348. The two pin differential gear at 348 includestwo differential gears 350, 352 connected to the reduced bearing pin354. A side shaft gear 358 is in rotatable engagement with thedifferential gears 350, 352. The bearing pins 354 are secured within anotch 361 of the differential housing 342. FIG. 6 discloses the threepin differential gear set 448. The three pin differential gear set 448includes three differential gears 450, 451, 452 connected to reducedbearing pins 454. A side shaft gear 458 is rotatably engaged with thedifferential gears 450, 451, 452. The bearing pins 454 are securedwithin a notch 461 of the differential housing 442 wall.

The improved torque distribution device 10 as described above createsseveral advantages over the prior art including the clutch pack runningwith and at axle speed which will reduce imbalance issues within thedrive train system. The minimized packaging requirement in the propshaft or drive shaft area also increases room needed for exhaust andfuel tank purposes. There is no separate oil housing necessary for theclutch pack as it is built within the differential housing and thelubricant used within the differential housing 42 is also used for theclutch pack 64. The device 10 reduces the effort needed for bearings andseals by being incorporated in the differential housing 42. This alsowill improve cooling of the torque distribution device 10 by using thesame lubricant or oil as found in differential drives. The combinationand inclusion of the torque distribution device 10 within thedifferential drive 22 also reduces the number of interfaces needed fromthe differential drive 22 to the power distribution portion of the drivetrain assembly. There is a reduction in weight because a torque transfercoupling and housing is no longer necessary and this also reduces costsby tooling fewer parts. Furthermore, the engagement mechanism whether itis a ball ramp mechanism or any other type of mechanism such aselectromagnetically engaged pilot clutches, etc., may be integrateddirectly into the differential drive 22. Furthermore, the combination ofboth front to rear axle control and right wheel to left wheel spincontrol in one unit greatly reduces the complexity of the drive trainsystem.

The present invention has been described in an illustrative manner, itis to be understood that the terminology which has been used is intendedto be in the nature of words of description rather than of limitation.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, within the scope of theappended claims, the present invention may be practiced otherwise thenas specifically described.

What is claimed is:
 1. A differential drive for use on a vehicle, saiddrive including: a rotatably driven differential housing supported in ahousing; a differential gear set arranged and supported in a housing; atorque distribution device adjacent to said differential gear set, saidtorque distribution device connects one of a differential side shaftgear with a side shaft, said torque distribution device includes aclutch pack, said clutch pack having a plurality of friction platesrotatably fixed with respect to said side shaft and a plurality offriction plates rotatably fixed with respect to one of said differentialside shaft gears, said torque distribution device arranged to controltorque between a front axle and a rear axle of the vehicle; a secondside shaft gear being driven with said same torque via said differentialgear set; and a second clutch pack engaged with said second side shaftgear and said differential housing.
 2. The differential drive of claim 1wherein said differential gear set includes two side shaft gearsarranged and supported in said differential housing.
 3. The differentialdrive of claim 2 wherein said differential gear set further includes atleast two differential gears which engage said side shaft gears and arerotatably supported in said differential housing.
 4. The differentialdrive of claim 1 wherein said differential gear set obtains a speeddifference between said front and rear axle and between a left and aright wheel of said rear axle at a predetermined time.
 5. Thedifferential drive of claim 1 wherein a differential gear operatesbetween said first and said second side shaft gears, said differentialgear allows vehicle wheels to spin freely.
 6. The differential drive ofclaim 1 wherein said second clutch pack provides a side to side lockingfunction.
 7. The differential drive of claim 1 further including a thirdplurality of friction plates adjoining said side shaft gear and saiddifferential housing to create a side to side locking effect.
 8. Thedifferential drive of claim 1 wherein said torque distribution devicecombines front to rear and side to side locking features.
 9. An improvedtorque distribution device for use on a vehicle drive train system,having an engine, a transaxle, a front and rear differential, apropeller shaft connecting the front and rear differential, a right andleft side shaft extending from each of the front and rear differentials,said improved torque distribution device comprising: the reardifferential having a differential gear set, said torque distributiondevice engaged with said differential gear set within a reardifferential housing; said torque distribution device including afriction clutch pack engaged with one of a side shaft gear and a sideshaft, said torque distribution device includes a clutch pack, saidclutch pack having a plurality of friction plates rotatably of fixedwith respect to said side shaft and said clutch pack having a pluralityof friction plates rotatably fixed with respect to one of said sideshaft gears, said clutch pack runs with axle speed and provides torquetransfer between said front and rear differential; and a second clutchpack in contact with side shaft gear and said rear differential housing,said second clutch pack provides a locking function to the left andright side shafts of the rear differential.
 10. The torque distributiondevice of claim 9 combining a front to rear and left to right side shaftlocking features in a single unit.
 11. A method of controlling thetransfer of torque between a front and rear axle of a vehicle, saidmethod including the steps of: locating a torque distribution deviceadjacent to a differential gear set in a differential housing;controlling said torque distribution device with a ball ramp mechanismand a motor; connecting one of a differential side shaft gear to a sideshaft via a clutch arrangement; and controlling torque transfer betweenthe front and rear axles by said differential side shaft gear.